>
> Currently, VMBus code initiates a VMBus unload in the panic path so that if a
> kdump kernel is loaded, it can start fresh in setting up its own VMBus
> connection.
> However, a driver for the VMBus virtual frame buffer may need to flush dirty
> portions of the frame buffer back to the Hyper-V host so that panic
> information is
> visible in the graphics console. To support such flushing, provide exported
> functions for the frame buffer driver to specify that the VMBus unload should
> not
> be done by the VMBus driver, and to initiate the VMBus unload itself.
> Together these allow a frame buffer driver to delay the VMBus unload until
> after
> it has completed the flush.
>
> Ideally, the VMBus driver could use its own panic-path callback to do the
> unload
> after all frame buffer drivers have finished. But DRM frame buffer drivers
> use the
> kmsg dump callback, and there are no callbacks after that in the panic path.
> Hence this somewhat messy approach to properly sequencing the frame buffer
> flush and the VMBus unload.
>
> Fixes: 3671f3777758 ("drm/hyperv: Add support for drm_panic")
> Signed-off-by: Michael Kelley <[email protected]>
Reviewed-by: Long Li <[email protected]>
> ---
> drivers/hv/channel_mgmt.c | 1 +
> drivers/hv/hyperv_vmbus.h | 1 -
> drivers/hv/vmbus_drv.c | 25 ++++++++++++++++++-------
> include/linux/hyperv.h | 3 +++
> 4 files changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c index
> 74fed2c073d4..5de83676dbad 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -944,6 +944,7 @@ void vmbus_initiate_unload(bool crash)
> else
> vmbus_wait_for_unload();
> }
> +EXPORT_SYMBOL_GPL(vmbus_initiate_unload);
>
> static void vmbus_setup_channel_state(struct vmbus_channel *channel,
> struct vmbus_channel_offer_channel *offer)
> diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h index
> cdbc5f5c3215..5d3944fc93ae 100644
> --- a/drivers/hv/hyperv_vmbus.h
> +++ b/drivers/hv/hyperv_vmbus.h
> @@ -440,7 +440,6 @@ void hv_vss_deinit(void); int hv_vss_pre_suspend(void);
> int hv_vss_pre_resume(void); void hv_vss_onchannelcallback(void *context); -
> void vmbus_initiate_unload(bool crash);
>
> static inline void hv_poll_channel(struct vmbus_channel *channel,
> void (*cb)(void *))
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c index
> 6785ad63a9cb..97dfa529d250 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -69,19 +69,29 @@ bool vmbus_is_confidential(void) }
> EXPORT_SYMBOL_GPL(vmbus_is_confidential);
>
> +static bool skip_vmbus_unload;
> +
> +/*
> + * Allow a VMBus framebuffer driver to specify that in the case of a
> +panic,
> + * it will do the VMbus unload operation once it has flushed any dirty
> + * portions of the framebuffer to the Hyper-V host.
> + */
> +void vmbus_set_skip_unload(bool skip)
> +{
> + skip_vmbus_unload = skip;
> +}
> +EXPORT_SYMBOL_GPL(vmbus_set_skip_unload);
> +
> /*
> * The panic notifier below is responsible solely for unloading the
> * vmbus connection, which is necessary in a panic event.
> - *
> - * Notice an intrincate relation of this notifier with Hyper-V
> - * framebuffer panic notifier exists - we need vmbus connection alive
> - * there in order to succeed, so we need to order both with each other
> - * [see hvfb_on_panic()] - this is done using notifiers' priorities.
> */
> static int hv_panic_vmbus_unload(struct notifier_block *nb, unsigned long
> val,
> void *args)
> {
> - vmbus_initiate_unload(true);
> + if (!skip_vmbus_unload)
> + vmbus_initiate_unload(true);
> +
> return NOTIFY_DONE;
> }
> static struct notifier_block hyperv_panic_vmbus_unload_block = { @@ -2848,7
> +2858,8 @@ static void hv_crash_handler(struct pt_regs *regs) {
> int cpu;
>
> - vmbus_initiate_unload(true);
> + if (!skip_vmbus_unload)
> + vmbus_initiate_unload(true);
> /*
> * In crash handler we can't schedule synic cleanup for all CPUs,
> * doing the cleanup for current CPU only. This should be sufficient
> diff --
> git a/include/linux/hyperv.h b/include/linux/hyperv.h index
> dfc516c1c719..b0502a336eb3 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -1334,6 +1334,9 @@ int vmbus_allocate_mmio(struct resource **new,
> struct hv_device *device_obj,
> bool fb_overlap_ok);
> void vmbus_free_mmio(resource_size_t start, resource_size_t size);
>
> +void vmbus_initiate_unload(bool crash); void vmbus_set_skip_unload(bool
> +skip);
> +
> /*
> * GUID definitions of various offer types - services offered to the guest.
> */
> --
> 2.25.1
